1. Field of the Invention
The present invention is directed towards a more efficient and less expensive process for biological treatment of aqueous waste and raw animal waste.
2. Background Art
A balanced nitrogen cycle is important to our environment. However, many human activities have perturbed the nitrogen cycle and caused nitrogenous pollution and environmental problems. Fertilizer production, farming of leguminous crops, and fossil fuel combustion contribute to an annual anthropogenic nitrogen fixation of 90, 40 and 20 Tg(N)/yr, respectively. Thus, the overall amount of nitrogen fixation contributed by human activity essentially equals the annual total of naturally-occurring nitrogen fixation, i.e., approximately 130 Tg(N)/yr.
Intake of high-nitrate food (e.g., highly fertilized vegetable, livestock fed with high-nitrate forage material or aquacultural production from an aqueous environment of high nitrate concentrations) has been correlated with increased risk to human health. Nitrate poisoning results from the conversion of nitrate to nitrite in the body. Absorption of nitrite into the blood stream produces abnormal hemoglobin (methemoglobin), which is incapable of transporting oxygen. Nitrates in water or meat are especially hazardous to young infants because their relatively high gastric pH facilitates the reduction of nitrate to nitrite by bacteria causing blue baby syndrome. Nitrite can interact with substrates such as amine and amide to produce N-nitroso compounds including nitrosamines, many of which may cause cancer in many animal species.
Ammonia (NH4+) is recognized as a toxic compound by the National Institute for Occupational Safety and Health (NIOSH) and the Occupational Safety and Health Administration (OSHA). A number of ammonium compounds, i.e., ammonium acetate, ammonium chloride, ammonium nitrate, ammonium sulfide, etc., are also toxic to human beings. Ammonium ions in drinking water, where ammonium ions exist in equilibrium with ammonia and hydrogen ions, may not only cause toxicity but also reduce the disinfecting efficiency of chlorine. Adding additional chlorine to compensate for the presence of ammonia will also cause over-disinfection problems such as producing by-products (e.g. trihalomethanes and total organic halogens), tastes and odors, accelerating corrosion, and increasing costs.
The present invention is directed to an efficient and cheap process of removing NH3/NH4+, NO2−, and NO3− from aqueous waste. The traditional biological treatment process uses oxidation methods to remove ammonium. However, oxidation of ammonium does not truly remove it but transforms it into NO2−, and NO3−, both of which still remain in the system. A biofilter system of the present invention utilizes an Alternating-Aerobic-Anoxic (AAA) process in a single biological fluidized bed reactor to provide efficient and cheap removal of carbonacious materials, nitrogenous materials and/or mixtures thereof from aqueous waste. This system has great economic advantages over other current nitrogen removal technologies and is believed to be the star of tomorrow. The biofilter system of the present invention is particularly suitable for treating aqueous waste resulting from aquaculture, industrial processes and animal husbandry.